Fill a large pot with water, add a pinch of salt, and bring it to a boil. Add the chopped broccoli rabe and blanch for about 1 to 2 minutes. Remove the broccoli rabe and set it aside. Then, add the pasta to the boiling water and cook until al dente. Reserve 1 cup of the pasta water when draining.

While the pasta cooks, heat olive oil in a large skillet over medium heat. Add the Italian sausage, breaking it up with a spoon, and cook until it is browned and cooked through, about 6 to 8 minutes.

Add the finely chopped garlic and crushed red pepper flakes to the sausage. Stir and cook for about 1 minute until the garlic becomes fragrant. Return the blanched broccoli rabe to the skillet and toss to combine.

Add the drained pasta to the skillet with the sausage and broccoli rabe. Toss everything together, adding the lemon juice, Parmesan, and a few tablespoons of the reserved pasta water (or more) to loosen the sauce to your desired consistency.

Season with kosher salt and freshly ground black pepper to taste. Serve hot with additional grated Parmesan cheese sprinkled on top.